My opinion ........Bigger is better concerning shotguns. Turkeys are best killed with head/neck shots using a minimum of #6 shot size. And , the more BB's the better. The old standard w/ CTG. shotguns is 1 1/4 oz. #5 shot. That's a High velocity load that kills most any small game excluding geese a flying. You got two choices to make a b/p shotgun perform like a CTG gun.........Equal shot and powder by volume , or slightly less shot , w/ the same powder volume as the first statement said. Should give slightly more velocity. And , let your pattern dictate the best load. My opinion , wouldn't use less than a 20 Ga. for turkeys. Fellow told me that one day , he hit 3 turkeys before he killed the fourth. Bad shooting??? , Wrong equipment , ??? , Think a little of both...............oldwood